代码之家 › 专栏 › 技术社区 › Neil N HLGEM

如何在小于、大于或等于之间动态切换?

Neil N HLGEM · 技术社区 · 16 年前

用户从下拉列表中选择比较类型(大于、小于、等于),然后输入要比较的大小(以字节为单位)。这就是我到目前为止所做的:

switch (cmboCompareType.SelectedText)
{
    case "Greater Than":
        fileOK = fi[i].Length > int.Parse(txtByteValue.Text);
        break;
    case "Less Than":
        fileOK = fi[i].Length < int.Parse(txtByteValue.Text);
        break;
    case "Equal To":
        fileOK = fi[i].Length == int.Parse(txtByteValue.Text);
        break;
}

有没有更优雅的方法来进行这种比较,而不用在C#中重复这么多代码?

8 回复 | 直到 16 年前

Brian Rasmussen 16 年前

int value = int.Parse(txtByteValue.Text);
int len = fi[i].Length;

switch (cmboCompareType.SelectedText)
{
    case "Greater Than": fileOK = len > value; break;
    case "Less Than": fileOK = len < value; break;
    case "Equal To": fileOK = len == value; break;
}

Jon Skeet 16 年前

两种选择:

1) 使用比较器和符号:

int requiredSign;
switch (cmboCompareType.SelectedText)
{
  case "Greater Than": requiredSign = 1; break;
  case "Less Than": requiredSign = -1; break;
  case "Equal To": requiredSign = 0; break;
  default: throw new ArgumentException();
}
fileOK = Math.Sign(fi[i].Length.Compare(txtByteValue.Text)) == requiredSign;

static readonly Func<int, int, bool> GreaterThan = (x, y) => x > y;
static readonly Func<int, int, bool> LessThan = (x, y) => x < y;
static readonly Func<int, int, bool> Equal = (x, y) => x == y;
...

Func<int, int, bool> comparison;
switch (cmboCompareType.SelectedText)
{
  case "Greater Than": comparison = GreaterThan; break;
  case "Less Than": comparison = LessThan; break;
  case "Equal To": comparison = Equal; break;
  default: throw new ArgumentException();
}
fileOK = comparison(fi[i].Length, int.Parse(txtByteValue.Text));

David 16 年前


var fileOK = new Dictionary<string, Func<int, int, bool>>
    (StringComparer.OrdinalIgnoreCase)
    {
        { "Greater Than", (x, y) => x > y },
        { "Less Than", (x, y) => x < y },
        { "Equal To", (x, y) => x == y }
    }[cmboCompareType.SelectedText](fi.Length, int.Parse(txtByteValue.Text));

John Kugelman Michael Hodel 16 年前

int actual = Math.Sign(fi[i].Length.CompareTo(int.Parse(txtByteValue.Text)));
int expected;

switch (cmboCompareType.SelectedText)
{
    case "Greater Than": expected = +1; break;
    case "Less Than":    expected = -1; break;
    case "Equal To":     expected =  0; break;
}

fileOK = (actual == expected);

Reed Copsey 16 年前

如果您有地图,您可以使用以下内容:

private int CompareOp(string Text)
{
    switch (cmboCompareType.SelectedText)
    {
        case "Greater Than": 
            return 1;
        case "Less Than": 
            return -1;
        case "Equal To": 
            return 0;
    }
}

// In your method:
fileOK = (fi[i].Length.CompareTo(value) == CompareOp(cmboCompareType.SelectedText);

Jeff Hornby 16 年前

public static int Compare(this int a, int b, string compareType)
{
    switch (CompareType)
    {
        case "Greater Than":
            return fi[i].Length > int.Parse(txtByteValue.Text);
            break;
        case "Less Than":
            return fi[i].Length < int.Parse(txtByteValue.Text);
            break;
        case "Equal To":
            return fi[i].Length == int.Parse(txtByteValue.Text);
            break;
    }
}

fileOK = fi[i].Length.Compare(int.Parse(txtByteValue.Text), cmboCompareType.SelectedTex);

Jeff Hornby 16 年前

您还可以将值-1、0、1添加到每个组合框项的value属性中,然后代码如下所示:

fileOK = fi[i].Length.CompareTo(int.Parse(txtByteValue.Text) == cmboCompareType.SelectedValue;

Neil N HLGEM 16 年前

我自己的想法,受Math.Sign()解决方案的启发。由于下拉框有三个值,其索引为0,1和2,我可以减去1得到-1,0,1,然后使用该值与符号进行比较,如下所示:

int sign = Math.Sign(fi[i].Length.CompareTo(int.Parse(txtByteValue.Text)));
fileOK = sign == (cmboCompareType.SelectedIndex - 1);

这取决于列表框中的项目是否按此特定顺序排列:
少于

当然,只有当这些是列表框中唯一的值时,才会起作用。也许不是最好的解决方案,但我发现我只用了两行代码就完成了这一点。

从技术上讲,我可以将其简化为一行代码:

fileOk=(cmboCompareType.SelectedIndex-1) == Math.Sign(fi[i].Length.CompareTo(int.Parse(txtByteValue.Text)));